CCleaner for Mac uses much of the same cleaning techniques used in CCleaner for Windows. This means that you get the same advanced cleaning for web browsers that you're used to in the Windows version. It also cleans many other Mac-only applications such as QuickTime Player.
What else does CCleaner for Mac clean?
Files related to the operating system like update files that sometimes take up a huge amount of space. Don't forget that the cleaning options get updated every month, so new apps are added regularly.